1. Field of the Invention
The invention relates generally to systems and methods for applying coatings, and more specifically to an intrinsically safe, multi-ported valve for controlling a hand-held combustion spray gun.
2. Discussion of Background Information
Combustion wire spray systems and processes are known for providing coatings on objects for various purposes. A typical combustion wire spray system includes a hand-held combustion spray gun that mixes oxygen, fuel gas, and air to melt a metal wire and spray the molten metal as a coating onto a target object. For example, a conventional combustion spray gun has a set of drive rolls powered by an air turbine that draw one or more metal wires into the gun. Oxygen and fuel gas are mixed in the gun and ignited to create a flame. Common fuel gases include acetylene, hydrogen, propane, methylacetylene-propadiene, or natural gas. Compressed air is used to shape and accelerate the flame at an air cap which includes an outlet nozzle. The metal wire is fed into the flame where it is melted and atomized. In this manner, molten droplets of the metal are propelled toward the object to be coated.
The sprayed-on molten metal solidifies on the object to form a coating that provides the surface of the object with one or more performance-enhancing characteristics. For example, combustion wire spray coating may be used for many applications, including but not limited to: corrosion protection, wear protection, surface restoration, electrical/thermal conductivity, decorative surfaces, etc.
Conventional air-powered combustion spray guns typically have a valve core for controlling the flow of various gasses, e.g., oxygen, fuel gas, and compressed air, through the gun. The valve core can be a rotary element that has various ports and passageways that, depending on the rotational position of the valve core, selectively control flow of the different gasses within the gun. For example, the valve core may be ported such that a plurality of gasses can be controlled simultaneously to achieve controlled flows for off, idle/ignite, and full flow operating conditions. Particularly, by rotating the valve core to a predefined position, ports within the valve core line up with gas passages in other parts of the gun. The diameters of the various ports in the valve core dictate the flow of each gas by acting as a flow-regulating orifice depending upon the supply pressure of each gas.
Typically, the position of the valve core is set by the operator using a valve core handle that extends from the combustion spray gun. When the operator rotates the valve core handle to a predetermined position corresponding to an operating condition, e.g., off, idle/ignite, full flow, etc., the valve core is positioned within the gun to provide a precise mixture of gasses for that operating condition. Generally, a spring-loaded detent mechanism maintains the valve core in each predetermined position. In this manner, the operator can set the operating condition of the gun using the valve core handle, and then release the valve core handle and use both hands for controlling the motion of the gun. Because the valve core stays in position once set, the gun will continue to emit a high velocity flame and molten metal until the operator turns the valve core handle to the off position. This can present a safety hazard, for example, in the case of a dropped gun that is operating at full flow.
Conventional air-powered combustion spray guns, such as those described above, do not have a mechanism for automatically stopping gun operation in case of an operator accident. Many electrically powered devices, from robots to hand-held power tools, have a safety “deadman” switch that cuts off electrical power to the device or tool when the switch is released by an operator. However, since hand-held air-powered combustion spray guns do not utilize electrical power, electrical deadman switches are not applicable to such combustion spray guns.
Moreover, known electrical emergency cutoff devices only provide for an on and off position. Hand-held air-powered combustion guns, on the other hand, require multiple position settings for different gas flow states. Additionally, since hand-held air-powered combustions guns should be lightweight to minimize operator fatigue, adding extra safety valves to an existing gun is not desirable.
Accordingly, there exists a need in the art to overcome the above-noted deficiencies.